Method of preparing wood for grinding



March 30, 1937. w DAVID 2,075,023

METHOD OF PREPARING woon FOR GRINDING Filed Dec. 12, 1934 r I I S nun-na R? R LE5 rE/e M. Del/l0 INFENTOR I I A TTORNEY atented Mar. 30, 1937aorsnzs METHOD OF PREPG WOUD FOR GRWG 7 Claims.

This invention relates to a method of and means for grinding wood forthe manufacture of news print paper. More particularly, the inventionrelates; first, to the treatment of the wood to render the fibersderived therefrom of longer length, greater in yield, stronger and oflighter color than is ordinarily obtained; and second, to a method ofassembling and grinding pieces of wood of irregular form and of varyingsize, and particularly pieces that are of small diameter; it 10 being anobject of this invention to provide a treatment for the wood that makespossible the production of fibers of such grade and color that theaddition of sulphite pulp is not required for the manufacture therefromof a superior grade of news print paper. Furthermore, it is an object ofthe invention to devise a method of grinding pieces of wood of irregularform so that there will be substantially no loss of tissue in the formof flour or slivers. Explanatory to the invention it will here be statedthat ground wood, as ordinarily produced for the manufacture of newsprint paper by grinding wood in a raw or natural condition, is made upof a mass of material in which short fibers predominate; these fibersconsisting of the torn fragments of the natural fibers of the Wood.Furthermore, due to the dark color of such fibers, as well as its lackof strength when made into paper, it is customary in making news printPaper under usual conditions, to add a certain proportion of sulphitepulp which is stronger, and of a lighter color. However, this additionof pulp incidentally increases the cost of manufacture of paper to apoint materially higher than would be the case if ground wood alone wereused.

Since this added expense is undesirable, it has been the principalobject of this invention, as was previously stated, to pr duce asuperior grade of paper without use of sulphite pulp, and to accomplishthis object I have provided a method of treating wood, before it isground, with certain chemical reagents dissolved in water which softensthe binding material, or middle lamellae of the cells or fibers innormal wood, and at the same time renders those dark colored, encrustingmaterials normally present in the wood more soluble in water, so thatthe wood when thus treated can be ground with the resulting productionof long, strong fibers that become -much lighter in color after washingin water than that produced from untreated wood.

Explanatory to another object of the invention, it is here stated thatheretofore, in the 55 manufacture of paper, attempts have been made togrind material of relatively small dimensions, but these attempts havenot been successful, mainly due to the difficulty attendant uponattempts to hold the material that is being ground against the surfaceof the grindstone. Therefore, it has been a further object of thisinvention to overcome this difliculty as fobllows: First, the materialthat is to be ground cleaned of all foreign matter and is barked, thenthe pieces are assembled in cars or other containers with the fibrousplant material disposed with the sclerenchymatous fibers presentingtheir main axes parallel to the longitudinal faces of the container. Thewood is then subjected to a chemical treatment to soften it, and aftertreatment the wood is compressed into compact bales to fit within thepocket of the grinder.

In accomplishing the before mentioned and other objects of theinvention, I have provided the improved mechanism as disclosed in theaccompanying drawing, wherein- Fig. 1 is a diagrammatic plan of aportion of a plant arranged for treating and grinding wood in accordancewith the objects of the present invention.

Fig. 2 is a cross section on line.22 in Fig. 1, showing the treatingretort.

Fig. 3 is a cross section of a press for compressing the treated Woodinto bales.

Fig. 4 is a perspective view of a bale removed from the press.

Fig. 5 is a sectional detail illustrating the placing of bales in agrinder.

Referring more in detail to the drawing- 8 designates what may be aconveyer whereby the wood selected to be ground for news print paper isconveyed to one or more barking drums 2 of a suitable kind. From thedrums the barked wood, cleaned of foreign matter, is discharged onto aconveyer belt 3 which passes between unloading platforms 3 adjacentwhich car tracks 5-5 extend.

The tracks 5 lead from the platforms through elongated, tubular retorts66 and there are cars or trucks i mounted for travel on these tracks,whereby the cleaned wood unloaded from the conveyer 3 and placed in thecars is conveyed into the retorts for the treatment previously recitedas an object of the invention.

The retorts are of a construction permitting them to be tightly closedand preferably are of circular cross section, as seen in Fig. 2, and thecars may be the usual wheeled trucks with cradle like bodies, as shown,in which the pulp wood is piled lengthwise for treatment. After a stringof trucks with wood piled thereon for treatment has been enclosed in aretort, the retort is filled with the chemical solution to a depthsumcient to cover the wood and the solution is placed 5 under pressurewhich is maintained until a specified amount of the solution has beenforced into the wood. The wood. may be completely impregnated with thesolution or only partially impregnated, dependent upon the particularcharacteristics of the paper which it is desired to produce.

In the present process the solution containing the chemical reagent isinjected into the wood at a temperature substantially below boilingpoint of water. The solution comprises water in which alkalies, such assodium carbonate and salts of acids, such as sodium sulphite, isdissolved. However, I do not limit the process to any particularconcentration of the chemical reagents in water as this is determined inmany cases by experiment only. The solution causes a certain chemicalreaction in the wood which softens and loosens the fibers. In the caseof woods that consist largely of sapwood and which are subject todiscoloration through the attack of such organisms as blue stain fungi,as for instance, various species of the genus Ceratostomella, I preferto use as a chemical reagent a substance or substances dissolved inwater that will inhibit the growth of such organisms, as for example,sodium carbonate.

After proper or desired impregnation of the wood has been effected, thehydraulic pressure is released and the solution is withdrawn from the 5retorts. Then steam, saturated or superheated, is admitted into theretorts at a pressure above atmosphere, and this is maintained until thechemical reagents with which the wood is impregnated have reacted on thewood and the 0 wood softened to the desired degree. The steam is thenallowed to escape from the receptacle and the treated wood is withdrawnby advancement of the cars along the tracks 5. The treated wood 5 s thenready for grinding and this may be done while it still is hot from thetreatment or it may b allowed to cool first.

It will be apparent that by controlling the pressure of the steam, orthe pressure and super- 5 heat of the steam and the duration of thetreatment, the rate of the reaction between the chemical reagent orreagents and wood, or such components of the wood that will react, canbe deflnitely controlled.

In the diagrammatic illustration, the storage tanks for the chemicalreagent are indicated at l0 and pumps for delivering it and forwithdrawing it from the retorts are indicated at II, while 42 and I3designate the pipe connections with 0 the pump. A steam generatingboiler is shown at I4 and this is connected to the retorts by a pipe 15.

After the wood has been treated in the retort as was heretoforedescribed, it is transferred to a mechanical, or hydraulic, press and iscompressed to an extent whereby all voids between individual pieces areclosed but without compressing the individual fibers of the pieces.While 70 held under compression wooden hoops are placed about thecompressed bales to hold them together when removed from the press.

In locating the wood in the press the pieces are laid lengthwise in themanner as heretofore described when placed in cars or containers fortreatment, and bales of standard size are formed so that they may beplaced in the standard types of grinding machines. In Fig. 3, I haveshown in cross section a bale being compressed in a press. In this view20 designates the wood pieces, 2| is the press chamber and ,22 theplunger actuated by a ram 23. Wooden hoops 24 are located in positionfor securing the bale after it has been fully compressed.

In' grinding, the bale is pressed against the stone as it revolves insuch manner that the direction of the axis of the stone is parallel tothe main axis of the lignified fibers present in the bundle, and thebale presents a maximum surface to the stone at all times.

Having thus described my invention, what I claim as new, therein anddesire to secure by Letters Patent is:-

1. A process of treating wood preparatory to grinding, comprisingbarking and cleaning the wood of foreign matter, enclosing the wood in aclosed container, filling the container with a chemical reagentsuificient to immerse the wood, applying pressure to the reagent toefiect its initial impregnation of the wood, draining the reagent fromthe container and applying steam under pressure to cause completeimpregnation of the wood.

2. A process of preparing wood for grinding, comprising cleaning thewood, treating it with a chemical solution for softening and looseningits fibers, bundling the wood and compressing the bundles into compactbales.

3. A process of preparing wood for grinding, comprising cleaning thewood of foreign material and bark, immersing the wood in a chemicalsolution under pressure to cause loosening and softening of its fibers,removing the solution and applying steam under pressure, then pressingthe wood into compact bales.

4. A Wood bale made up of chemically softened wood pieces, compressedtogether in a compact bale wherein the fibers of the wood pieces extendsubstantially in parallel relation.

5. A wood bale made up of wood pieces of irregular size and compressedtogether in a compact bale to remove all voids between adjacent piecesand wherein the fibers of the pieces extend substantially parallel andlengthwise of the bale.

6. A bale as recited in claim 5 wherein wooden bands bind the baletogether.

7. A method of preparing wood for grinding comprising, barking andcleaning the wood, conveying it into a closed container, applying achemical solution to the container under pressure to cause an initialimpregnation of the wood, withdrawing the solution and applying steamunder pressure to complete the impregnation, withdrawing the wood, andcompressing it while hot into bales wherein the fibers of the woodpieces are laid substantially parallel and lengthwise of the bale.

LESTER W. DAVE).

